The invention relates to a zeugmatography process according to the preamble of patent claim 1. Such methods for the imaging of the interior of bodies utilizing the phenomenon of nuclear magnetic resonance (NMR) have become known under the designation of zeugmatography, spin-imaging, spin-mapping, or FONAR. However, the known methods have a very small signal-to-noise ratio, so that, on account of the long measuring duration therefore resulting, the medical apparatus is uncertain.
Methods for imaging of the nuclear spin density of specific isotopes (most frequency hydrogen) in the interior of bodies, specifically, medically significant distributions in the interior of the human body, have been described, e.g. by P. Lauterbur (1973), P. Mansfield and I. L. Pykett (1978), R. Damadian et al (1976), W. S. Hinshaw (1974), as well as A. Kumar et al (1975), and Z. Abe et al (1974). (Complete citation of these references is found at the end of the Detailed Description, under the heading "Literature References".) These methods can also be employed in order to obtain information regarding physical and chemical conditions and their change in the interior of bodies, such as e.g. chemical composition and metabolism, as well as through-flow rate and speed of flow. Use is here made of the phenomenon of nuclear magnetic resonance. The body to be examined is exposed for this purpose to a constant (D.C.) magnetic field B.sub.o and the nuclear isotopes to be detected are excited to precession by a high frequency field B.sub.1 of the angular frequency EQU .omega..sub.o =.gamma.B.sub.o
where .gamma. is the gyromagnetic ratio of the corresponding nuclei. Customarily, the transverse component of the precessing magnetization is then detected by means of induction.
The detected signal is proportional to the precessing magnetization M.sub.o which, in turn, is proportional to the primary magnetic field B.sub.o and to the precession frequency .omega..sub.o.
Thus, for a good signal-to-noise ratio, as high as possible a constant field B.sub.o and hence also as high as possible a measuring frequency is desired. Conflicting with this is the finite conductivity of the body to be examined; i.e., for medical application, that of a biological body. On account of the known skin-effect, namely, the high frequency field, exciting the nuclear resonance, varies over the cross section of the measurement object. It is thus no longer guaranteed that the precession angle for the excited nuclear spin is approximately constant over the body cross section. Moreover, the signal contributions from the marginal zones and the interior zones of the body to be examined are detected with varying intensity. In an assessment of Bottomley and Andrew (1978), it is shown that imaging-nuclear magnetic resonance processes for medical diagnostic total body imaging at frequencies above 10 MHz (in the case of protons corresponding to constant fields greater than 0.25 T) are seriously impaired by the skin effect. However, according to Hoult and Lauterbur (1979), it can be predicted therefrom that, in the case of the permissible measurement frequencies, images having satisfactory signal-to-noise ratios necessitate exposure times which lie in the range of minutes; however, particularly for applications in medical diagnostics, shorter exposure times would be desirable on account of unavoidable body movements.